Currently, gas chromatography is widely used for separation, identification, and determination of the chemical components of a mixture. Mass spectrometry (MS) is also widely used to qualify and quantify the composition, the structure, and isotopic ratios of various chemical samples. Frequently, it is valuable to use gas chromatography to separate the chemical components of a mixture and then use mass spectrometry to detect and analyze those chemical components. The benefits of combining these two techniques has lead to the creation of gas chromatograph-mass spectrometer instruments. In the standard setup of these instruments, the sample is introduced to the gas chromatograph first, where it is separated in the gas chromatograph analytical column. Following separation, the components are transported from the analytical column to the mass spectrometer for analysis.
Historically, gas chromatograph-mass spectrometers have been large instruments with substantial power requirements. Due to these size and power requirements, gas chromatograph-mass spectrometers have typically been limited to the laboratory. Presently, however, there is an increasing demand for portable gas chromatograph-mass spectrometers that can be used both in and out of the laboratory. Recently, the development of low thermal mass gas chromatographs and miniature mass analyzers has made portable gas chromatograph-mass spectrometers possible.
One common problem associated with gas chromatograph-mass spectrometers is that samples introduced into a gas chromatograph-mass spectrometer may contain chemical impurities at concentration levels many times that of the analytes of interest within the samples. When the samples are introduced into the analytical column of the gas chromatograph-mass spectrometer, these impurities tend to collect at the beginning of the analytical column. Over time, as the level of impurities on the column increases, the performance of the gas chromatograph-mass spectrometers diminishes.
Historically, the only remedy for this problem was to cut off sections of the analytical column as part of periodic maintenance. For large gas chromatograph-mass spectrometers, removal of sections of the analytical column may be a viable option. For newer portable gas chromatograph-mass spectrometers, however, this option is less viable because the analytical column is smaller and usually integrated into the overall assembly in such a way that sections cannot be removed.
More recently, guard columns have been used as an alternative remedy to the contamination problem. Guard columns are short inert columns or small diameter, e.g. capillary, tubings placed at the beginning of the analytical column. When guard columns are used, the impurities will instead be deposited in the guard column as opposed to the analytical column. Guard columns are designed to be relatively inexpensive and easily replaceable, such that when the guard columns become overly contaminated or fouled, they can then be quickly removed and replaced.
Because the guard column is connected to the analytical column, it is important to be able to control the temperature of the guard column so as not to adversely affect the transport of the volatilized sample. In the case of portable gas chromatograph-mass spectrometers, this temperature control must also be achievable without significantly increasing the size or power consumption of the instrument. In addition, the method of temperature control cannot affect the ease of replacing the guard column after it becomes overly contaminated. Present guard columns have not provided such temperature control within these limitations. Therefore, there is a need for a guard column for gas chromatograph-mass spectrometers that meets all these requirements.